Transcript Chapter 11 Complex Inheritance and Human Heredity

Chapter 11 Complex
Inheritance and Human
Heredity
11.1 Basic Patterns of Human
Inheritance
1
Recessive Genetic Disorders
Mendel’s work went unnoticed by the scientific
community for about 30 years then it was
rediscovered in the early 1900s.
 At that time many scientists were interested in
the cause of diseases and noticed that some
diseases “ran in families”.
 Alkaptonuria was the first identified (recessive)
genetic disorder. Alkaptonuria, from an enzyme
deficiency, causes black acidic urine and later in
life affects bones and joints.

2
Recessive Genetic Disorders
 A recessive trait is
expressed when the
individual is
homozygous recessive
for the trait.
 Both parents would
need to have at least
one recessive allele.
 Usually the parents
are heterozygous
(carriers) for the
disorder.
3
4
Cystic Fibrosis
Affects the mucus-producing glands,
digestive enzymes, and sweat glands
 Chloride ions are not absorbed into the
cells of a person with cystic fibrosis but
are excreted in the sweat.
 Without sufficient chloride ions in the
cells, a thick mucus is secreted

5
Cystic Fibrosis
6
Cystic Fibrosis
7
Albinism
Caused by altered genes, resulting in the
absence of the skin pigment melanin in
hair and eyes
 White hair.
 Very pale skin
 Pink pupils

8
Albinism
9
Tay-Sachs Disease
Caused by the absence of the enzymes
responsible for breaking down fatty acids
called gangliosides
 Gangliosides accumulate in the brain,
inflating brain nerve cells and causing
mental deterioration.
 Death by age 2

10
Dominant Genetic Disorders
99.9% of population is homozygous recessive for achondroplasia
11
Huntington’s Disease





Affects the nervous
system
Latent disorder
affects age 30 to 50
Gradual loss of brain
function (“holes” in
brain)
Genetic test available
Result of allele
mutation at tip of
chromosome #4
12
Achondroplasia
Most common form of
dwarfism
 75% of individuals
born to parents of
average size, result of
new mutation
 Lethal spontaneous
abortion in
homozygous
dominant genotype

13
Pedigree Analysis
14
Pedigree Analysis






Are females
Are males
Shaded in circles and
squares are affected
individuals
Roman Numerals (I –
IV) are generations
Lines across
represent mating
Lines down
represent offspring
15
Pedigree Analysis



Count the number of
affected males and affected
females. If most males and
few or no females most
likely sex linked trait.
Look at the affected
individuals. If every
individual with the trait has
a parent with the trait then
this trait is dominant. If
non-affected parents
produce an offspring with
the trait then it is recessive.
Determine the phenotype
and genotype of every
individual
16
Pedigree Analysis






Affected males: 1
Affected females: 2
(not sex linked)
No affected individual
has parent with the
trait, means recessive
All affected individuals
would be homozygous
recessive, aa
All parents of affected
individuals would be
heterozygous, Aa
Siblings of affected
individuals would be
heterozygous (Aa) or
homozygous dominant
(AA)
17
Pedigree Analysis
18